Influence of the orientation of Ti–Al interphase boundary on the mutual diffusion rate at the solid and liquid states of aluminium: molecular dynamics simulation

The influence of the orientation of Ti-Al interphase boundary on the intensity of mutual diffusion at solid-phase and solid-liquid-phase contacts was studied by the method of molecular dynamics. Four orientations of the boundary with respect to the Ti (hcp) and Al (fcc) lattices were considered: (0001) : (111), (0001) : (001), $(10\bar{1}0)$ : (111), $(10\bar{1}1)$ : (001). At solid-phase contact, an important phenomenon influencing the intensity of mutual diffusion was the formation, due to the mismatch of the lattices of Ti and Al, of grain boundaries in Al parallel to the interphase boundary. This boundary was both the main source and sink of structural defects, including vacancies required for diffusion to proceed. In the case of solid-liquid-phase contact, after melting of aluminium, part of it near the interphase boundary remained in the crystalline state, repeating the titanium lattice. That is, the boundary between the crystal and the liquid metal was shifted by two or three atomic planes deep into the aluminium. For the considered orientations, concentration curves were obtained after simulating mutual diffusion at different temperatures. The flatter parts of the curves, which are responsible for the diffusion of Ti atoms deep into liquid Al, turned out to be similar for all orientations. However, the parts related to the diffusion of Al atoms into crystalline Ti were different: diffusion of Al atoms in Ti proceeded more intensively with the orientation of the boundary (0001) and more slowly with the orientations $(10\bar{1}0)$ and $(10\bar{1}1)$.